1. Field of the Invention
This invention relates to a magnetic recording apparatus wherein a recording amplifier is coupled to a magnetic head by a transformer. The invention is directed to an improvement for recording all information without any omission of information on a circular track of a magnetic disk.
2. Description of the Prior Art
Referring to FIG. 5 (circuit configuration) and FIG. 6 (operation), a prior art in an electronic still camera system is explained.
In FIGS. 5 and 6, an output terminal of a recording amplifier 1 is connected to a source voltage Vcc through a primary coil of a step-up transformer 2. A magnetic head 3 is connected to a secondary coil. A frequency modulated (FM) luminance signal Y-FM and a frequency modulated chrominance signal C-FM are input to recording amplifier 1 through a mixer 4. An input terminal of a play-back amplifier 5 is AC coupled to the primary coil by a condenser 6.
A magnetic head 3 is used for recording and reproduction. The recording amplifier 1 and the play-back amplifier 5 are controlled by a control circuit 7. A recording switch 8 and a rotation phase detector 9 for a video floppy disk are connected to the control circuit 7. The phase detector 9 outputs a PG signal, i.e. one pulse per one rotation of the video floppy disk.
When the switch 8 is turned on, the circuit 7 generates a trigger pulse 11 (FIG. 6) which overlaps one pulse 10-1 of a PG pulse sequence 10. In a term (one vertical scanning period: 1V) between the pulse 10-1 and a pulse 10-2 just after the pulse 10-1, a control pulse 12 out of the circuit 7 goes to a high level, and an output of the recording amplifier 1 turns on. Accordingly a recording current I.sub.1 with a bias DC current flows into the primary coil of the transformer 2. As a result, a recording current I.sub.2 flows into the magnetic head 3, and a still video signal is recorded on a circular track of the video floppy disk.
However, because of a transformer coupling between the recording amplifier 1 and the magnetic head 3, when the amplifier 1 is turned off, after the recording current I.sub.2, a transient current 14 flows into the magnetic head 3 which is the result of a back electromotive force.
Since the transient current 14 operates as an erasing current, a top part of an already recorded information is erased by the current 14 and the information is missed.